Quote:
Originally Posted by Newtownian
I checked out Baader and other sites and cant see any 0.1 nm Bandpass at 656 nm.
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You are missing the point. There does not exist any single filter that can give you the 0.1nm resolution required to view the specific Hydrogen Alpha wavelength.
The etalons previously described uses two plates that reflect the light back and forth within a narrow gap, which when tuned to a resonant frequency, allows light of a specific wavelength (with a narrow band) through. Any wavelength outside the tuned interval is "rejected".
Wikipedia have an excellent article on the subject ->
http://en.wikipedia.org/wiki/Fabry%E...interferometer
Note that this relates to the etalon only. You will also need a blocking filter, which takes everything outside the Ha band and blocks it, allowing viewing of only the desired wavelength. Note that the blocking filter also screens out potential harmful wavelengths that still pass through the etalon (think harmonics).
OIC!